The present invention is directed to an arrangement for producing an optical coupling between a plurality of first optical waveguides and a plurality of second optical waveguides.
In IOCs, which can be integrated optical circuits, planar optical waveguide circuits or hybrid optical circuits, there is often the task of coupling a plurality of waveguides, which usually have identical spacing between their axes, to optical fibers or to other optical waveguide circuits. This task is particularly difficult when the spot diameters of the optical wave guided in the waveguides are extremely small and, moreover, do not match with the spot diameters of the optical waves guided in the optical fibers or the second optical waveguide circuit which is to be coupled to the first group.
Typical spot diameters of an optical wave having a range of 1.3 .mu.m through 1.5 .mu. wavelength lie at 10 .mu.m when guided in a monomode optical fiber. By contrast, waveguides of IOCs, particularly when formed of a III/V material system, which includes GaAlAs or InGaAsP, have a typical spot diameter of 2 .mu.m. In order to achieve a good coupling efficiency, the spot diameters must be matched to one another, for example by optical lenses or tapers, and the positions of the spots must be adjusted extremely precisely relative to one another. The above-recited spot diameters, for example, require a lateral adjustment precision of approximate .+-.0.5 .mu.m for the axis of the waveguide of the IOCs with respect to the fiber spot, which has been demagnified with the lens or a taper, and an axial adjustment in the axial direction of approximately 2 .mu.m.
An arrangement for producing an optical coupling between a plurality of waveguides of an IOC and a plurality of optical fibers have been suggested. In one of these arrangements, the fibers are arranged and held in V-channels that are fashioned in the surface of a carrier member. The fibers are, thus, held so that they end before an edge of the member so that end surfaces or end faces of the fibers are arranged at a distance from this edge. Depressions for accepting and holding spherical lenses are fashioned in the surface between the edge and the end faces of the fibers at a distance from these end faces. Each of these depressions has a rectangular cross section and tapers pyramidally in the direction perpendicular to the surface and toward the inside of the carrier member from a maximum diameter to a minimum diameter which is greater than zero. A connecting trench is constructed in the surface of the carrier member between every end face of the fiber and the conical depression fashioned in front of this end face. This connecting trench assures an undisturbed propagation of the optical wave between the spherical lens held in this depression and this end face.
The waveguides of an IOC end at an edge of the surface of the substrate on which they are integrated, so that the end faces of these waveguides lie at this edge. The edge of the IOC is arranged just opposite the edge of the carrier member for the fibers so that every end face of the waveguide of the IOC lies opposite an end face of the fibers. Thus, a spherical lens is situated between every pair of end faces lying opposite one another.
The carrier member for the fibers of this known arrangement is composed of silicon, wherein the V-channels, the connecting trenches and the conical depressions are produced by preferential etching. Width and depth of the etched structures can typically observed with a precision of approximately 1 .mu.m. This is adequate for the positioning of the fibers vis-a-vis the lenses. However, approximately 0.5 .mu.m must be demanded for the positional precision of the lenses with respect to the axes of the IOC. Underetching of the mask employed for the manufacture of the etched structure or a non-uniform etching rate over the surface of the carrier member of silicon, however, may lead to significantly greater deviations of these centers of the spherical lenses from their desired and prescribed position. This method, thus, does not seem suitable for satisfying the extreme tolerance demands that are made thereon. Another disadvantage is that the packing density of the waveguides is limited by the relatively large spherical lenses having a diameter of .gtoreq.250 .mu.m.
An arrangement for producing an optical coupling between a plurality of waveguides of an IOC and a plurality of optical fibers has likewise already been proposed, wherein every end face of a waveguide of the IOC has an end of an end section of a fiber tapering taper-like toward this end lying opposite it.
In this arrangement, the fibers are arranged and held on a surface of a carrier member with the taper-shaped end section of the fiber freely projecting beyond the edge of the surface of the carrier member. The positions of the ends of the taper-shaped end sections are defined by an aperture mask. This aperture mask is composed of a plate arranged between the waveguides of the IOC and the fibers and has one flat surface facing toward the waveguides and one flat surface facing toward the fibers. Through holes of the masks, which extend from one flat surface to the other, are fashioned in the plate, and these through holes conically taper from the flat side or surface facing toward the fiber in the direction toward the flat side facing toward the waveguides of the IOC from a maximum diameter that is larger than the diameter of the fibers to a minimum diameter that is smaller than or equal to the diameter of the ends of the taper-shaped end sections.
The plate is composed of a silicon wafer wherein the through, conical holes are produced with privileged or preferential etching. The advantage is that the center of the holes can be extremely precisely defined with planar technology. Lateral deviations of the centers of the holes from the desired position can occur if the sides of the walls of the pyramidally conical holes are etched at different speeds (the positions of the holes are defined on the flat side of the silicon wafer facing away from the waveguides of the IOC) or in that the etching mask employed is asymmetrically underetched. The greatest errors in the position of the ends or tips of the taper-like end sections, however, probably occur when small blow-outs of at least 1 .mu.m appear at a contacting location of the taper-shaped end section with the plate in the hole or when the taper-shaped end section itself has asymmetries. Both these are especially problematical.